What is the length of line segment EF if DE is 6ft and DF is 11ft and angle FDE is 40 degrees

The length of EF = 7.48 feet

Step-by-step explanation:

* Lets consider these tree segment formed triangle DEF

- We have the length of two sides and the measure of the

including angle between these two sides

* So we can use the cos Rule to find the length of the third side

- The cos rule ⇒ a² = b² + c² - 2bc cosA

# a is the side opposite to angle A

# b is the side opposite to angle B

# c is the side opposite to angle C

# Angle A is the including angle between b and c

* In the problem

∵ DE = 6 feet

∵ DF = 11 feet

∵ m∠FDE = 40° ⇒ including angle between DE and DF

and opposite to EF

- By using cos Rule

∴ (EF) ² = (DE) ² + (DF) ² - 2 (DE) (DF) cos∠FDE

∴ (EF) ² = (6) ² + (11) ² - 2 (6) (11) cos (40)

∴ (EF) ² = 55.882133 ⇒ take square root for both sides

∴ EF = 7.47543 ≅ 7.48 feet

* The length of EF = 7.48 feet